Not a glitch or weird but certainly a design error…
There is no other menu that appears as a mouseover popup (all the others need to be clicked). That’s inconsistent UX.
If you do keep it as a popup, it should appear above everything. At the moment, all the other menus appear above it.
You can fix that with
.custom-header-dropdown {
z-index:9999;
}
Although, the stacking context might (should) offer a better means of fixing that problem.
And, if it is kept as a popup, it’s not really a dropdown which is how it is named in the CSS class, custom-header-dropdown. Semantics are important.